This invention relates generally to filling and sealing intravenous solution bags and, more particularly, to a method and apparatus for filling intravenous solution bags in a sterile, sealed enclosure and sealing the bags by vibration welding.
Previously, intravenous solution bags have been filled in clean rooms under hoods capable of maintaining sterile conditions within specified limits. The bags are sterilized before being taken into the room to prevent the room from being contaminated, and they are re-sterilized after being filled to ensure sterility of the bag as shipped. However, some solutions are damaged if the bags are sterilized after being filled. Thus, the bags must be processed in a very sterile environment to prevent contamination during the filling and sealing processes so that re-sterilization is not required. Clean rooms capable of maintaining the necessary sterile environment are expensive to build and operate. Further, these rooms are highly inefficient because everything in the room, including any workers, must be sterilized before entering the room.
Conventional intravenous solution bags are made of thermoplastics such as vinyl. Usually, the opening through which the bag is filled is sealed by heating the bag in the vicinity of the opening to a temperature sufficient to melt portions of the bag and then pressing the melted portions of the bag together as they cool to weld the opening shut.
Several methods have been used to heat the bag. One such method is radio frequency welding in which high frequency electromagnetic radiation is directed toward the bag to heat the plastic. If any solution is present on the outside surface of the bag, electrical arcing can occur which may damage the bag and/or the radio frequency welding machine. Another method of sealing the bag is ultrasonic welding in which a portion of the bag is clamped between a sonic horn and an anvil. The horn vibrates against the bag at very high speeds (e.g., 20-40 kHz or more). As the horn vibrates, it moves toward and away from the bag and heats the bag, first at the outside surface and then farther inward. Because the outside surface of the bag is heated first and the inside surface must be melted to weld the opening shut, the bag melts through its entire thickness during ultrasonic welding. Melting weakens the bag and prevents it from being suspended from above the weld. Therefore, the bag must be supported both below the weld to prevent it from rupturing and above the weld to prevent it from spilling. Further, the operating parameters used in ultrasonic welding must be closely controlled or inferior welds are made. Thus, ultrasonic welding is difficult to perform consistently.